This protocol continues implementation of a laboratory model to evaluate pharmacological agents potentially useful in the treatment of cocaine abuse, investigating problems relevant to understanding and reducing uncontrolled cocaine use. It focuses on the smoked route, since crack use is now the major cocaine problem in the United States, and evaluates, within the context of cocaine self-administration, behavioral mechanisms of action of pharmacological agents proposed for treating cocaine dependence. Twenty subjects, ten opioid-dependent and ten non-opioid-dependent, will be recruited. Memantine is a non-competitive NMDA antagonist widely used in Europe in recent years as a treatment for dementia syndromes and Parkinson's disease. The study will require 47 days, with 21 days conducted on an inpatient basis and additional outpatient examinations.